1. Field of the Invention
The present invention generally relates to the fibers used in consolidated fiberboard products and methods for producing such fibers. More specifically, this invention relates to a method wherein the raw materials to be refined may be any of a number of generally non-recyclable contaminated woods, plastics, and papers which are then co-refined at elevated temperatures in high pressure steam to form thermoplastic-coated lignocellulose fibers that are suitable for consolidation into a variety of fiberboard products.
2. Description of the Prior Art
Waste disposal is an ever-increasing concern to society. Although recycling efforts have been relatively successful with a variety of materials, certain materials have continually posed a problem as being generally non-recyclable. Examples of these hard-to-recycle materials include "urban wood waste" such as demolition waste from old buildings, urban wood chips generated from construction materials, old pallets and boxes, and the like. Yet, it is believed that useful fiberboards could be produced from these materials if a means for recycling and refining these problematic materials could be found.
Generally speaking, the prior art has been successful in producing lignocellulose fibers from wood chips. In particular, U.S. Pat. No. 2,757,115 to Heritage teaches the production of lignocellulose fibers from wood chips and other lignocellulose waste products, such that the resultant fibers are useful for forming felted fiberboard products. Heritage forms the fibers by subjecting the lignocellulose material to pressurized steam while concurrently being rubbed and abraded. The steam acts to soften the lignin at the surface of the lignocellulose material, which is then rubbed or abraded away, thereby exposing the interior of the material which is likewise softened and abraded. This is repeated until the chip has been reduced to a fiber, which can then be pressed into felted fiberboard products. Although Heritage's teachings are useful for the formation of wood fibers from "green" wood waste products, i.e., wood products having a relatively high moisture content, or correspondingly with a solids content of about 40% to 50%, these teachings do not aid in the refinement of "urban wood waste" which is typically very dry, having a solids content of at least about 80% or more. In addition, Heritage required the use of relatively high horsepowers for refinement of the moist wood chips, because the temperature of the steam used for refining the lignocellulose material remained essentially only at the boiling temperature of water due to the continual vaporization of the moisture within the green wood chips.
Alternatively, U.S. Pat. No. 2,872,337 to Heritage et al. teaches the production of coated lignocellulose fibers for forming a coated felted fibrous mat. The lignocellulose fibers are generally produced by the method described above in the Heritage '115 patent; however, after the fibers are abraded, they are transported by the steam and mixed with a suitable thermosetting resinous binder so as to result in coated lignocellulose fibers which are useful for consolidating into fiberboard.
The shortcoming associated with the Heritage '115 patent is that, again, the teachings are limited to wood chips having relatively high moisture levels, and again, they require the use of relatively high horsepowers for the refinement of the wood chips. In addition, although they are producing coated fibers, they are doing so by utilizing virgin raw materials, i.e., virgin polymeric binder material with virgin wood chips.
Therefore, as can be readily appreciated by those skilled in the art, both Heritage patents tend to be relatively limited in the materials which can be processed in that they are limited to relatively high moisture content wood and if applicable, a virgin polymeric binder material. Furthermore, both Heritage patents utilize a process which involves relatively high horsepower requirements during refining.
Therefore the need exists for a relatively low horsepower process for refining wood chips, which can utilize a variety of the generally non-recyclable contaminated materials, such as dry wood chips from urban wood waste, which may be optionally combined with a suitable thermoplastic.
Accordingly, what is needed is a process for forming lignocellulose fibers which may be optionally thermoplastic-coated, and which are suitable for consolidation into a fiberboard product, wherein the starting materials can include a variety of materials, including generally non-recyclable wood, paper, and/or plastic products, and wherein the process does not require high horsepower loads during refinement of the chips.